Is Summation of Higher Order Partial Derivatives in LaTeX Correct?

[AOA]

I know writing $$\frac{\partial^{1}u}{\partial x^{1}}$$ is "bad" notation, but can I still write the sum:

$$\sum^{n}_{k=1}\frac{\partial^{k}u}{\partial x^{k}}$$

??

THANK YOU

PS. Being able to write LaTeX equations is actually awesome.

 

[CompuChip]

When you write it explicitly it looks a bit weird, but I see no objection to using it in such a sum.

 

[AOA]

OK. I just wanted to make sure. Thanks!

 

[denisv]

Can I ask what kind of situation you're getting that sum in?

 

[arildno]

While uncommon, I don't see anything bad about it.

When dealing with just the first derivative of some function, it is superfluous, but completely analogical to the case that $x=x^{1}$
Neither of these two notations are "bad" in any way.

 

[HallsofIvy]

I would even accept
$$\sum_{k=0}^n \frac{\partial^k u}{\partial x^k}$$
with the understanding that
$$\frac{\partial^0 u}{\partial x^0}= u(x)$$